WASHINGTON (CNN) -- A congresswoman said Thursday that her "jaw dropped" when military doctors told her that four in 10 women at a veterans hospital reported being sexually assaulted while in the military.

Lance Cpl. Maria Lauterbach said she was raped by a fellow Marine. A Marine has been charged in her death.

A government report indicates that the numbers could be even higher.

Rep. Jane Harman, D-California, spoke before a House panel investigating the way the military handles reports of sexual assault.

She said she recently visited a Veterans Affairs hospital in the Los Angeles area, where women told her horror stories of being raped in the military.

"My jaw dropped when the doctors told me that 41 percent of the female veterans seen there say they were victims of sexual assault while serving in the military," said Harman, who has long sought better protection of women in the military.

"Twenty-nine percent say they were raped during their military service. They spoke of their continued terror, feelings of helplessness and downward spirals many of their lives have taken since.

"We have an epidemic here," she said. "Women serving in the U.S. military today are more likely to be raped by a fellow soldier than killed by enemy fire in Iraq."

As of July 24, 100 women had died in Iraq, according to the Pentagon.

In 2007, Harman said, only 181 out of 2,212 reports of military sexual assaults, or 8 percent, were referred to courts martial. By comparison, she said, 40 percent of those arrested in the civilian world on such charges are prosecuted.

Defense statistics show that military commanders took unspecified action, which can include anything from punishment to dismissal, in an additional 419 cases.

But when it came time for the military to defend itself, the panel was told that the Pentagon's top official on sexual abuse, Dr. Kaye Whitley, was ordered not to show up despite a subpoena.

"I don't know what you're trying to cover up here, but we're not going to allow it," Rep. Henry Waxman, D-California, said to the Defense official who relayed the news of Whitley's no-show. "This is unacceptable."

Rep. John Tierney, the panel's chairman and a Democrat from Massachusetts, angrily responded, "these actions by the Defense Department are inexplicable."

"The Defense Department appears to be willfully and blatantly advising Dr. Whitley not to comply with a duly authorized congressional subpoena," Tierney said.

An Army official who did testify said the Army takes allegations of sexual abuse extremely seriously.

"Even one sexual assault violates the very essence of what it means to be a soldier, and it's a betrayal of the Army's core values," Lt. Gen. Michael Rochelle said.

The committee also heard from Mary Lauterbach, the mother of Lance Cpl. Maria Lauterbach, a 20-year-old pregnant Marine who was killed in December, allegedly by a fellow Marine.

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Mary Lauterbach said her daughter filed a rape claim with the military against Marine Cpl. Cesar Laurean seven months before he was accused of killing her. Watch dead Marine's mom demand change »

"I believe that Maria would be alive today if the Marines had provided a more effective system to protect the victims of sexual assault," she said.

In the months after her daughter filed the rape claim, she said, the military didn't seem to take her seriously, and the onus was on "Maria to connect the dots."

"The victim should not have the burden to generate evidence for the command," Lauterbach told the Subcommittee on National Security and Foreign Affairs. "Maria is dead, but there will be many more victims in the future, I promise you. I'm here to ask you to do what you can to help change how the military treats victims of crime and to ensure the victims receive the support and protection they need and they deserve."

Another woman, Ingrid Torres, described being raped on a U.S. base in Korea when she worked with the American Red Cross.

"I was raped while I slept," she said.

The man who assaulted her, she said, was a flight director who was found guilty and dismissed from the Air Force.

Fighting back tears, Torres added, "he still comes after me in my dreams."

The Government Accountability Office released preliminary results from an investigation into sexual assaults in the military and the Coast Guard. The GAO found that the "occurrences of sexual assault may be exceeding the rates being reported."

"At the 14 installations where GAO administered its survey, 103 service members indicated that they had been sexually assaulted within the preceding 12 months. Of these, 52 service members indicated that they did not report the sexual assault," the GAO said.

The office found that the military and Coast Guard have established policies to address sexual assault but that the implementation of the programs is hampered by an array of factors, including that "most, but not all, commanders support the programs."

"Left unchecked, these challenges can discourage or prevent some service members from using the programs when needed," the GAO said.

Tierney said, "what's at stake here goes to the very core of the values of the military and the nation itself.

"When our sons and daughters put their lives on the line to defend the rest of us, the last thing they should fear is being attacked by one of our own."